Opening application menu when modal dialog is active makes Quit entry stuck in disabled state

Background:

When a modal dialog is opened, Quit entry in application menu is disabled, so you can't close an app using this entry or Cmd+Q shortcut.

Problem:

If you open an application menu with modal dialog opened, to check that Quit entry is indeed disabled, or if you press Cmd+Q, triggering Quit action, it gets shy and stays in disabled state forever.

Steps:

1. Run attached project (or any project with modal windows)
2. Open a modal dialog
3. Open application menu (the one with About/Preferences/Quit/...), see that Quit is disabled. Alternatively, press Cmd+Q, which should do nothing because modal dialog is shown.
4. Close modal dialog

ER: Quit entry in application menu is enabled back, Cmd+Q shortcut closes application

AR: Quit entry in application menu is still disabled, Cmd+Q does nothing

If you omit step 3, not opening application menu when modal dialog is shown, everything works fine and Quit is re-enabled as it should.